The proposed study will utilize data from an ongoing, epidemiologically-derived, prospective longitudinal study to test whether early indices of temperament predict the emergence of Attention Deficit/Hyperactivity Disorder (ADHD) in 1st grade. Data will be drawn from an ongoing developmental epidemiological study that utilized a prospective longitudinal design (i.e., the Family Life Project; NIH 1P01HD396667-01A1, Vernon-Feagans, PI). The proposed study is unique in utilizing a multi-informant, multi-method approach, which does not rely on parent reports, for measuring temperamental reactivity and regulation across the first three years of life. Individual differences in temperamental reactivity and regulation will be used as predictors of parent and teacher-reported ADHD in 1st grade. In addition to testing for the aggregate risk of ADHD from temperament, the proposed study will also test Nigg and colleagues (2004) hypotheses regarding five distinct temperamentally mediated pathways into combined type ADHD. This raises the prospect that the strength of the association between specific dimensions of temperament and ADHD may vary across subgroups of children and is consonant with a larger effort in the literature aimed at clarifying the etiologic plurality of ADHD.